A laser scanner is a device used for information storage, retrieval, input and output with maximum potential today, and the successful application of laser printers and facsimile apparatus further invites the related technical R&D on the laser scanner by technicians. Among several scanning technologies, the polygon mirror scanner plays a considerably important role in a great number of devices. A series of continuous scanning lines are generated through the rotational reflection of a polygon mirror. Its capability of achieving rapid linear scanning, simple structure and remarkably wide angle of deflection just meet the application requirements for printer and facsimile apparatus. However, in order to improve the scanning resolution and the scanning speed, increasing the rotation velocity of the co-axial driving motor of the polygon mirror may be put into practice but the bearing of said motor will be subject to relative wear and the polygon mirror as a whole tends to wobble. Another approach is to increase the facet number of the polygon mirror, but this will require longer system length and also reduce the scanning angle. Therefore, some innovative ideas have been proposed. According to the literature concerned, there are at least two systems: one of them is to make use of a multi-frequency acousto-optic modulator wherein a composite signal of more than two frequency components is applied to the driver, the emitted light will be diffracted into more than two beams to project onto the polygon mirror to generate a number of scanning lines in juxtaposition simultaneously and the modulating signal may be applied to each scanning line as shown in FIG. 1; another proposal is to make use of a multiple light source device to generate a group of incident light beams in parallel such as the laser diode array or a light emitting diode array. The foregoing two systems all reflect a plurality of incident beams through one mirror facet of the polygon to a photo-conductive drum to generate a multi-beam scanning and each incident beam has to be able to be modulated separately, so their driving circuits are inevitably very complex and their costs are considerably expensive.
In view of the above, this inventor, in order to eliminate the foregoing drawbacks, has developed an improved structure of a high-resolution polygon mirror laser scanner through his research and design for a number of years.
The primary object of this invention is to offer an improved structure of a high-resolution polygon mirror laser scanner which is characterized by simple structure and higher scanning speed so as to achieve the purpose of high-resolution scanning through a few beam splitters which separate the single beam emitted from an acousto-optic modulator into more than two beams, a few mirror reflectors which project each beam onto the mirror facet of a polygon mirror, and a cylindrical lens which focuses and projects these beams onto a photo-conductive drum.